Hydrolysed cereal proteins have a high commercial value. They are used in a wide variety of food products, feed products, cosmetics and industrial applications such as for example glues or paints.
Hydrolysed cereal proteins can be produced through acid hydrolysis, for example as described in EP 0 363 771, or through enzymatic hydrolysis.
The enzymatic hydrolysis may be done by adding enzymes to a protein containing substrate in aqueous suspension and by incubating this blend, for example as described in WO 02/32232.
Enzymatic hydrolysis may also be done in a two steps process: a liquefaction step to liquefy the incoming protein material and an incubation step where the actual hydrolysis is taking place. Both steps of the process typically comprise a continuous back mixing. In both steps back mixing is a disadvantage.
In the liquefaction step, as a result of the back mixing, part of the incoming proteins is constantly recycled and remains in the liquefaction step for a longer period of time than desired. Other incoming protein material leaves the liquefaction step too early as they by-pass the back mixing. This material arrives in a non-liquefied state in the incubation step.
In the incubation step, as a result of the back mixing, some material is constantly recycled and is incubated for a longer period of time than desired, resulting in highly hydrolysed proteins, having a low to very low molecular weight. Other material leaves the incubation step too early and is therefore poorly hydrolysed.
Thus existing hydrolysis processes have the disadvantage that the end product (the hydrolysate) does not contain hydrolysed proteins which have been equally hydrolysed, especially when the starting material has visco-elastic properties and forms lumps when hydrated, such as vital wheat gluten. Next to hydrolysed proteins having the desired molecular weight, the hydrolysate typically contains poorly hydrolysed or non hydrolysed proteins having a high molecular weight, and highly hydrolysed proteins having a low to very low molecular weight, such as amino acids.
The low molecular weight fraction of the hydrolysate can confer a bitter taste to the hydrolysate, which is undesirable for food and feed applications. The high molecular weight fraction is often responsible for phase separation (for example due to sedimentation) when the hydrolysate is brought into suspension. This is not desirable, especially when the hydrolysate is used to make products which need to mimic the behaviour of milk-like emulsions.
The hydrolysis of proteins having visco-elastic properties is very difficult due to lump formation upon hydration. So far, lump formation can only be avoided by adding dried vital wheat gluten in solutions comprising for example processing aids.
Another disadvantage of the existing processes is that usually high processing volumes and times are required.
There is thus need for an improved process for producing hydrolysed cereal proteins wherein the proteins have been hydrolyzed to a same degree of hydrolysis and therefore do not have above mentioned disadvantages.